Internet DRAFT - draft-badra-eap-peer-credential-protection
draft-badra-eap-peer-credential-protection
Internet Engineering Task Force M. Badra
LIMOS Laboratory
Expires: July 2007 January 23, 2007
EAP Peer Credential Protection
<draft-badra-eap-peer-credential-protection-00.txt>
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Abstract
Actual EAP methods provide authentication services based on the use
of certificates, secret keys or passwords. These methods, excepting
the tunneling ones, exchange peer identity in clear text. Moreover,
some of these methods do not enable the ability to exchange channel
binding information. They do not, however, define a common encoding
of the credential protection or of the channel binding or of. This
document defines AVPs to securely exchange data related to the peer
identity, when an EAP method deriving keys is deployed.
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1 Introduction
It is required that EAP methods deriving keys provides for mutual
authentication between the EAP peer and the EAP server. Peer
authentication requires exchanging data related to their identity.
Even though EAP tunneled authentication protocols protect such data,
existing widely deployed EAP methods such as EAP-TLS are not able to
protect data related to the peer identity.
Actual EAP methods provide authentication services based on the use
of certificates, secret keys or passwords. Except EAP tunneled
authentication protocols, these methods exchange peer identity in
clear text.
According to RFC 3748, EAP methods SHOULD have the ability to derive
exportable keying material. This document defines a set of AVPs
transporting identity related data, and securely exchanges them
using the derived key.
Attribute-value pairs (AVPs) provide a way to exchange arbitrary
information between peer and EAP server within a secure channel.
This document defines two AVPs (AVP Code TBS): AVP Identity-
Protection-Certificate and AVP Identity-Protection-Sharedkey to
carry data related to the peer identity. It is defined as following:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Code (TBS) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Data field of each AVP in the format is described in Section 2.
1.2 Requirements language
The key words "MUST", "MUST NOT" and "MAY" in this document are to
be interpreted as described in RFC-2119.
2 EAP methods with authentication based on certificates
For EAP methods requiring authentication based on certificates (e.g.
EAP-TLS) initially establishes a server authentication and then
exchanges an AVP of type Identity-Protection-Certificate carrying
data related to the peer identity, as long as an evidence proving
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the identity of the peer that holds the certificate and the
corresponding private key.
The evidence used here is the same defined by the security protocol
itself (e.g. IKE2, TLS, etc.).
2.1 AVP Data field: case EAP-TLS
In the case of EAP-TLS, the peer sends the AVP Identity-Protection-
Certificate once the TLS Handshake is complete. The AVP data content
is the same of the TLS certificate verify message that defined in
RFC 2246. The AVP MUST be sent immediately after exchanging the TLS
finished messages.
The server that sends the TLS certificate request message MAY deny
the peer access in the case where the peer does not transmit an AVP
carrying a valid certificate.
The following sequence illustrates the operation of the EAP-TLS
protocol with AVP Identity-Protection-Certificate.
Peer Authenticator
| |
| PPP EAP-Request/ |
| EAP-Type=EAP-TLS |
| (TLS Start) |
|<-----------------------------------------------------|
| |
| PPP EAP-Response/ |
| EAP-Type=EAP-TLS |
| (TLS client_hello) |
|----------------------------------------------------->|
| |
| PPP EAP-Request/ |
| EAP-Type=EAP-TLS |
| (TLS server_hello |
| TLS certificate, |
| [TLS server_key_exchange,] |
| [TLS certificate_request,] |
| TLS server_hello_done) |
|<-----------------------------------------------------|
| |
| PPP EAP-Response/ |
| EAP-Type=EAP-TLS |
| (TLS client_key_exchange, |
| TLS change_cipher_spec, |
| TLS finished) |
|----------------------------------------------------->|
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| |
| PPP EAP-Request/ |
| EAP-Type=EAP-TLS |
| (TLS change_cipher_spec, |
| TLS finished) |
|<-----------------------------------------------------|
| |
| PPP EAP-Response/ |
| EAP-Type=EAP-TLS |
| (AVP |
| [TLS certificate, |
| TLS certificate_verify]) |
|----------------------------------------------------->|
| |
| PPP EAP-Success |
|<-----------------------------------------------------|
2 EAP methods with authentication based on shared keys
Many EAP methods use shared key and passwords to establish a mutual
authentication as long as to derive material keys. A set of these
methods, such as EAP-AKA and EAP-SIM uses pseudonym approach
allowing the peer to use a fresh identity/key if the peers wish to
avoid having their identity unprotected.
Two cases MAY be takes with pseudonym management:
1- centralised authentication server
2- decentralised authentication server.
This document does not consider the decentralised authentication
server case, due to existing deployment reasons.
The pseudonym management in this document consists of sharing two
identities with two shared key; the first is permanent and the
second is ephemeral.
When an EAP method based on shared key is deployed, the peer will
use the ephemeral identity during the authentication phase.
If the server does not recognise the peer ephemeral identity, both
the peer and the server reuse the permanent identity.
At the end of the EAP method exchange, the server will send to the
peer an AVP Identity-Protection-Sharedkey carrying a new identity
and a new shared key. Thus, EAP methods implementing the AVP defined
by this document MUST replace the ephemeral identity with the
identity transmitted by the server.
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The following exchanges show where the server does not recognises
the peer ephemeral identity:
Peer Authenticator
| |
| PPP EAP-Request/ |
| EAP-Type=XXX |
| (XXX massages) |
|<---------------------------------------------------------|
| |
| PPP EAP-Response/ |
| EAP-Type=XXX |
| (XXX messages
| Ephemeral ID) |
|--------------------------------------------------------->|
| |
| PPP EAP-Request/ |
| EAP-Type=XXX |
| (XXX massages |
| Alert: Unrecognized ID) |
|<---------------------------------------------------------|
| |
| (XXX messages |
| Permanent ID) |
|--------------------------------------------------------->|
| |
| .. sequence of EAP-Request/Response with EAP-Type=XXX .. |
|<-------------------------------------------------------->|
| |
| PPP EAP-Request/ |
| EAP-Type=XXX |
| (XXX massages |
| (AVP |
| [Ephemeral ID, |
| shared key]) |
|<---------------------------------------------------------|
| |
| PPP EAP-Response/ |
| EAP-Type=XXX |
|--------------------------------------------------------->|
| |
| PPP EAP-Success |
|<---------------------------------------------------------|
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The following exchanges show where the server recognises the peer
ephemeral identity:
Peer Authenticator
| |
| PPP EAP-Request/ |
| EAP-Type=XXX |
| (XXX massages) |
|<---------------------------------------------------------|
| |
| PPP EAP-Response/ |
| EAP-Type=XXX |
| (XXX messages
| Ephemeral ID) |
|--------------------------------------------------------->|
| |
| .. sequence of EAP-Request/Response with EAP-Type=XXX .. |
|<-------------------------------------------------------->|
| |
| PPP EAP-Request/ |
| EAP-Type=XXX |
| (XXX massages |
| (AVP |
| [Ephemeral ID, |
| shared key]) |
|<---------------------------------------------------------|
| |
| PPP EAP-Response/ |
| EAP-Type=XXX |
|--------------------------------------------------------->|
| |
| PPP EAP-Success |
|<---------------------------------------------------------|
7 Security Considerations
The security considerations described throughout [TLS] and [EAPTLS]
apply here as well.
References
[TLS] Dierks, T. and C. Allen "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[EAP] Aboba, B., et. al., "PPP Extensible Authentication
Protocol EAP)", RFC 3748, June 2004.
[EAPTLS] Aboba, B., and D., Simon, "PPP EAP TLS Authentication
Protocol", RFC 2716, October 1999.
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Author's Addresses
Mohamad Badra
LIMOS Laboratory - UMR (6158), CNRS
France Email: badra@isima.fr
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Acknowledgment
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Funding for the RFC Editor function is currently provided by the
Internet Society.
Badra Expires July 2007 [Page 8]
